Protecting tube for thermocouples



April 20, 1954 J. v: HART PROTECTING TUBE FOR THERMOCOUPLES Filed Oct.18, 1950 INVENTOR JOH N V. HART ATTORNEY.

Patented Apr. 20, 1954 UNITED ATENT OFF ICE PROTECTING TUBE FORTHERMOCOUPLES poration of Delaware Application October 18, 1950, SerialNo. 190,895

6 Claims. 21

This invention relates to wells for holding heat sensitive elements suchas-thermometers or thermocouples in substances of various kindsundergoing treatment involving temperature change. This inventionrelates more specifically to an improved corrosion-resisting well whichis alsoresistant to the adherence of metallic oxides or zcokey deposits.This invention is useful particularly with molten aluminum, whichrapidly destroys the well or protecting tube which sur rounds thetemperature-measuring element, or with substances. containing othercorrosive components or coke-forming constituents, for example,hydrocarbon oils undergoing cracking.

In measuring the temperature of molten aluminum and in the cracking ofhydrocarbon oils where corrosive compounds are present, which, in themost prevalent forms, are particularly destructive of pure iron or steelof which the bulk of the apparatus in this sort of equipment iscomposed, it is necessary to protect the walls of the vessels and pipesfrom these compounds.

In addition to the comparatively short life, due to corrosion, of thehitherto known thermometer wells in the presence of molten aluminum orcorrosive compounds, another objection presents itself in that metallicoxides or cokey or carbonaceous constituents tend to adhere to ordinarythermometer wells made of iron or steel. A coating or mass of thecarbon-like material is thus formed upon the thermometer well whichmass, since it is a poor conductor of heat, renders the thermometer muchless sensitive to temperature changes of the substance underobservation.

The particular object of this invention is therefore to provide asuitably constructed well of durable material which will not only beresistant to corrosion but will also repulse the adherence of oxides ormetal or cokey or carbon- 1 like constituents of hydrocarbons.

More specifically, it is an object of this invention to provide aprotecting well or tube composed of welded steel pipe closed at one endwith a plug punched out of steel and covered with a layer of gray ironcast over the outer surface of the steel pipe and steel plug andadhering thereto and of a uniform thickness.

The various features of novelty which characterize this invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, its advantages and specific objects obtained with its use,reference should be had to the accompanying 2 drawings anddescriptivematter in which is illus trated and described a preferredembodiment of the invention.

In the drawings:

Fig. l is a side elevation with parts broken away in vertical,longitudinal cross section.

Fig. 2 is a vertical, transverse cross section on line 2-2 of Fig. l asviewed in the direction of the arrows.

A heat sensitive element generally indicated at I is formed of a helicalcoil of wires 2 and 3 of different metals or different metalliccompositions joined at one'end to form a hot junc tion 4. These wirespass through ceramic insulators 5 to a terminal head, generallyindicated at 6, whence they are connected to lead wires which are ledoff through a pipe I to a suitable indicating instrument.

In order to protect the heat sensitive element I from mechanical damageor the ruinous effects of heat or corrosion, the temperature sensitiveelement l is surrounded by a protecting tube, sheath, or well, generallyindicated at 8. Well 8 is composed of a welded steel pipe 9 which isclosed at its outer or immersed end (surrounding temperature sensitiveelement I) by a plug [0 punched from a sheet of steel. Steel pipe 9 andsteel plug ID are covered on their outer surface with a gray ironcasting !2 of uniform thickness.

Attempts were made to form the well of cast iron by casting with a sandcore in a sand bed. It was found that sand cores of this type tended towarp and shift, which produced finished castings whose wall thicknesswas not uniform, thereby reducing the life expectancy of the finishedwell. Where the iron layer I2 is cast directly on the surface of thewall tube 9 and the steel plug in the result is an integral tube whosewalls are of uniform thickness. The outer or open end of the tube isscrew threaded at i3 to interfit with the terminal head ii.

While, in accordance with the provisions of the statutes, I haveillustrated and described the best form of the invention now known tome, it will be apparent to those skilled in the art that changes may bemade in the form of the apparatus disclosed without departing from thespirit of the invention as set forth in the appended claims, and that insome cases certain features of the invention may sometimes be used toadvantage without a corresponding use of other features.

Having now described my invention, what I 3 claim as new and desire tosecure by Letters Patent is as follows:

1. A protective casing for a temperature sensitive element including, ahollow tube, a plug closing one end of said tube, and a protectivecoating cast on the outer surface of said tube and said plug to resistoxidation or corrosion or adhesion of deposits from the material Whosetemperature is being measured and in which the closed end of the casingis immersed.

2. A protective casing for a temperature sensi-- tive element including,a welded steel pipe, a plug punched from steel closing at one end ofsaid pipe, and a layer of gray iron cast on and adheringto the outersurface of said pipe and said plug so as to form therewith an integralcasing for insertion in the material whose temperature is to bemeasured.

3. A well for a heat sensitive element including, a tubular memberhaving a closed end adapted to protrude into the material whosetemperature is being measured and composed of an inner layer of steeland an outer layer of cast iron adherent thereto by reason of theshrinkage of the outer layer of cast iron upon cooling in contact withthe inner layer from a molten state.

1. A protective well for a heat sensitive element including, a metaltube, a closure for one end of said metal tube, and a layer of cast grayiron adhering to the outer surface of said tube and said member, thebond between said layer of cast grey iron and the outer surface of saidtube and said member being a shrink fit resulting from depositing moltengrey iron directly upon the outer surface of said tube and said memberand allowing said layer of grey iron to harden by cooling in directcontact with the outer surface of said tube and said member.

5. A protective casing for heat sensltiveelemerits including, a metalpipe, a metal plug closing one end of said pipe, and a layer of castgray iron of uniform thickness cast from a molten state directly on andadhering to the outer surface of said pipe and said plug.

6. A protecting tube adapted to extend through an opening to be exposedto the heat ofa space whose temperature is to be measured, saidprotecting tube being adapted to enclose a thermocouple and having anopen end from which the thermocouple wires are led and a closed endadapted to be immersed in the material whose temperature is to bemeasured, said tube being composed of a welded steel pipe, a steel plugclosing the end of said pipe, and a layer of gray cast iron of uniformthickness adhering to the outer surface of said pipe and of said plug,said pipe and said plug forming a core on which said layer of grey ironis cast directly from a molten state.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Foxboro Company, Bu1letin l98, page 19 (1937). BristolCompany Catalog 1402, pagesv 48-49 Brown Instrument Company, Catalog#1102 (1937) pages 4445. a

